1. Field of the Invention
The present invention generally relates to acoustic devices and more particularly to a method of manufacturing multiple frequency resonator devices.
2. Description of Related Art
Wireless communication devices are utilizing an ever-increasing number of frequency bands, such as PCS frequencies for cell phones, GPS frequencies for location, and ISM frequencies for data or other utilities. Sometimes, a user would want to communicate across many bands from one device, perhaps even through a single antenna. For instance, a single cell phone could provide phone service at 900 MHz and utilize a Bluetooth radio at 2400 MHz to provide a hands-free, wireless link to a headset. Therefore frequency selection devices (such as filters or resonators used in voltage controlled oscillators) will be required to manipulate different RF bands, at widely varying frequencies, preferably within a single device.
Ideally these frequency selection devices would be integrated xe2x80x9con chipxe2x80x9d with active circuit elements such as transistors in an effort to develop a xe2x80x9csingle chip radioxe2x80x9d solution. Such integration is driven by a desired increase in capability and performance, coupled with a desired reduction in size and part-count of such a device.
One technology that is a leading candidate for on-chip frequency selection is thin-film, bulk acoustic wave, RF-filter technology. At the heart of this technology, a piezoelectric thin film is placed between conducting electrodes to form a thin film resonator (TFR). Frequency selection is done acoustically. For example, a circuit provides an RF signal to introduce sound waves into the piezoelectric film, and the mechanical resonance of the sound waves in-turn affects the electrical properties seen by the circuit.
TFRs are often used in electronic signal filters, more particularly in TFR filter circuits applicable to a myriad of communication and microelectronic technologies. For example, TFR filter circuits may be employed in the aforementioned cellular, geo-location and data communications, as well as in wireless and fiber-optic communications, computer or computer-related information-exchange or information-sharing systems.
As briefly noted above, the piezoelectric material in these TFRs converts electrical to mechanical energy and vice versa, such that at its mechanical resonance frequency, the electrical behavior of the device abruptly changes. Electrical signals of particular frequencies easily pass thorough the resonators, while others will not be transmitted. These particular frequencies can typically be dictated by choosing resonator size and design. Resonators of certain sizes and design frequencies can be networked in appropriate combinations, such that they will impose desired filtering functions on signals passing through the network.
Accordingly, as a TFR is an acoustically resonant device, the thickness and material properties of the piezoelectric film, together with the thickness and material properties of the electrode films in intimate contact with the piezoelectric film, determine at what frequency the resonance will occur. Conventionally, to build a device for frequency selection at multiple and quite separated, frequencies, the artisan typically deposited multiple piezoelectric films of quite different thicknesses on a substrate and/or electrode film. These multiple depositions were costly and also posed a formidable process control challenge, since the films required are quite specializedxe2x80x94they all had to be composed of a piezoelectric material.
Further, conventional manufacturing techniques have used different metals in order to fabricate single-frequency resonators, but have not used combinations of metals for well-separated frequency operations on a single die, with a single piezoelectric layer.
In accordance with the present invention, there is a method of forming a multiple frequency resonator device having a single piezoelectric layer. In one aspect, differing metallic electrodes or differing thickness electrodes are formed at different locations on a support structure and/or on a single thickness film of piezoelectric material. The resultant device contains multiple frequency resonators having greatly separated acoustic resonance frequencies therethrough. These multiple frequency resonators can then be combined to form a bank of frequency selective devices in order to handle the many different RF bands, at widely varying frequencies, that wireless communication technologies demand today.